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Dec. z, 1926.

R. S. BAILEY TELEPHONE SYSTEM Sheet 1 1+ five/770m- Rand 51 54/79 2 Sheets- Filed Oct. 11. 1922 Dec. 7 1926.

' 1,609,395 R. s. BAILEY TELEPI'IONE SYSTEM Filed CS1. 11, 1922 Rama S. 54 78} Patented Dec... "'7', l92.

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BAND S. BAILEY, 0F MONTCLAIB, NEW JERSEY, ASSIGNOB, '10 AMERICAN TELEPHONE lint-@ 395 AND TELEGRAPH COMPANY, A CQEPOBATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed Gctober 11, 1922. Serial No. 593,850.

This invention relates to telephone systems and more particularly to systems wherein subscribers lines terminate at a plurality of operators positions so that a call emanating from such a subscribers station may be attended to by any one of a plurality of operators.

It is an object of this invention to improve the means for excluding an operator from access to a subscribers line when a call on said line is being handled by another operator. I

Another object of this invention is to in form an operator when she has attempted to answer a call over a subscribers line, that the call is already being attended to by another operator.

The foregoing objects are obtained in accordance with one feature of this invention by the provision, in a cord circuit, of a sleeve relay which is controlled through a normally closed contact of .a slow-to-operate answering supervisory relay, and which operates when the cord is connected with a busy line, thereby preventing the connection of the oeerators telephone set with the cord circuit.

Another feature of this invention is the provision of a circuit arrangement such that the battery supply -is disconnected from the answering plug of the cord circuit when such cord is connected with a busy line thereby preventing the operation of the supervisory relay.

A still further feature is the provision of a circuit rrangement whereby signals are given at both the answering and calling ends of the cord circuit when the cord is connected to a busy line.

The manner in which the foregoing obleets and features are effected will be readily understood from the following detailed description taken in reference to the accompanyiug drawings in which Figure 1 shows one embodiment of the invention and discloses a calling subscribers station. a fourpar v line and a cord circuit for interconnecting the calling station with the fourpai y' line. Fig. 2 shows another embodiment of the invention and also discloses a calling subscribers station, a four-party line and an interconnecting cord circuit.

in the following detailed description, it will-be assumed that a subscriber at the, station on line is the calling. subscriber and one of the parties on the four-party line B is the called subscriber.

Upon initiating a call, the subscriber at station A removes the receiver from the switchhook and establishes an energizing circuit for line relay 3 which may be traced from grounded battery through the righthand winding of relay 3, inner armature and back contact of cut-off relay l, line conductor 5., over the subscribers line loop line conductor 6, outer armature and back contact of cut-ofl relay 4, and thence to ground, through the left-hand winding of line relay 3. Relay 3, in perating cOmpleteS a circuit extending from grounded battery through the armature and front contact of relay 3, conductor 7, and thence to ground through the filaments of the line lamps 8, 9 and 10, which lamps are located in front of different operators at a central offiie, any one of which operators may answer the call. The lamps are illuminated in the circuit just traced thereby notifying all the operators that a call is awaiting attention.

It will be assumed at this time that the operator at the position at which amp 10 is located, is free to handle the incoming call. This operator, therefore, inserts the plug '11 associated with the cord circuit C into jack 12 located at her position and associated with the calling subscribeifs line.

Upon the insertion of plug 11 into ack 152, an ener 'izing circuit for slow-operating supervisory relay 13 is established which is traced from grounded battery through the lowermost armature and back contact of relay 14, lower left-hand winding of repeating coil 15, winding of relay 18, ring contacts of plug 11 and jack 12, over the subscribers line loop, tip contacts of jack 12 and plug 11, upper lefthand windi g of repeating coil 15, and upper arm e and bacl: contact of relay M to ground. Relay l3 thereupon operates and disconnects the discriminating test relay 16 from the sleeve of the cord circuit and substitutes therefor the regular sleeve relay 1?. Relay 17 thereupon operates in the circuit just established extending from grounded battery through the winding of relay 17, conductor l8 armature and front contact of relay l8, sleeve contacts of plug 11 and jack 12, sleeve conductor 19 and thence to ground throughthe winding of cut-off relay l. Relays enere,

connects the position register 20 to the cord circuit whereupon the position register is operated over a circuit extending from grounded battery through the operating windings of the register 20, conductor 22,

inner lower armature and front contact of relay 17, conductor 23, and thence to ground througl'i the inner lower arn'iature and back contact of relay 21.

It is thought unnecessary in this descript-ion to go into detail as to the object and operation of the position register 20, as this apparatus does not enter into the invention.

ihe operator then ascertains from the calling subscriber the nature of the call and upon learning that a suliiscriher on line 13 is desired inserts the calling plug 24 associated with cord circuit G into the jack 25 associated with the four-party line B.

Vhen plug 24 is inserted in jack 25, an energizing circuit established for relay Bl, extending from grounded battery, through the winding of relay 21, sleeve conductor 26, sleeve contacts of plug 24 and jack 25 to ground through the winding of cut-off relay 75. Relay 21 upon energizing disconnects at its lowermost and uppermost armatures and back contacts, the operators telephone set from the talking conductors of the cord circuit and at its inner lower armature and back contact disconnects the position register 20 from the cord circuit. At its inner up 701 arnuiture and front contact, relay Ql completes a circu'i for the pick-up interrupter X. w 'di may he traced from grounded hatter ugh the interrupter when the hr of such inter raptor rests on a live se cent thereof, conductor 527, break contat s 01'? relay 28, conductor 29, outer arn'iature and back contact of relay conductor 30, winding of relay 28, conductor 31, and thence to ground through the inner upper armature and front contact of relay Relay energizes in this circuit and establishes a locking circuit for itself which. may be traced. from grounded battery, through theinner armature and front contz'ict of relay 52S, conductor 29, outer armature and back contact of relay 32, conductor 30, *inding of relay 28 and conductor 31, to ground, through the inner upper armature and front contact of relay 21. Relay 28 at its outer armature and front, contact,- interconnects the conduetors 44 and 60 for ringing purposes to be hereinafter described.

delay 21, in operating, as previously mentioned, closes its make contact to ground, thereby establishing a circuit extending from grounded battery through the winding of relay 33, conductor 34, armatures and back contacts of relays 32 and 35, conductor 36, make contact of relay 21, and thence to ground, through the. inner upper armature of relay 21. Relay 33 energizes in the circuit just traced, thereby connecting the con-- doctors of the subscribers line B with the conductors 48 and 49 which are associated with the party ringing keys 1W, J, R and The called line B is now conductively a,- sociated with the conductors of the cord circuit in such a manner as to permit the transmission of signaling current over the called line by the operation of any one of the keys M, J, R, or

The system disclosed in the drawing is designed for four-party semi-selective signal' and the manner in which the called parties are signalled may he readily understood froin the following description.

Assuming that the party \V on line B is desired, the operator will actuate the ring ing key "N and in so doing grounds the tip conductor of the cord circuit at the ri 'ht-hand contacts of key V The key at its left-hand contacts 45 establishes a circuit extending from the one-ring signaling source associated with the interrupter Z, over conductor 64, left-hand armature and back contact of relay 41, conductor 49. uppermost armature and back contact of relay 14, conductor 43, winding of relay 35. conductor 44-, contacts 45 of key V condoctor 46, left-hand normal contacts of key R conductor 47, right-hand normal, con tacts of key J conductors 3'7 and 48, lowermost armature and front contact of relay 33, ring contacts of plug :24 and jar 2:), ring conductor of the line ll, andv thence to ground. through the operating windings oi the. bells located at the stations V and R. It is to be noted here that the ringing current source at Z transmits a onering signal-- ing current and the party at R supposed to heed only a two-ring signal so that this party will ignore the ringing oi" the hell at t time. whereas the party at W will rose; the one-ring signal and proceed to answer the call.

If pa ty R is the called-for euhscriber. the operator actnates key R and. in so doing. places around on the right-hand contact other R thereby establishing an energizing circuit tori-nay 41, which may be traced from grounded batterythroush the inner armature and front contaetoit relay 28, conductor Q9, outer armature and back Contact of relay 32, conductor 30, winding of relay l1, conductors 61 and 62, and thence to ground, through the right-hand contacts 63 of key It. gizes and disconnects the one-ring signaling source at Z from conductor 4 and substitutes therefor the tworing signaling source at Y which transmits ringing currentover a circuit extending from the grounded source at Y. conductor 10, right and lefthand armatures and front contacts of relay -11, conductor 42, upper armature and back contact of relay 14%, conductor 6L3, winding of relay 35, conductors 4 1 and 66, outer right-hand armature and front contact of relay 28, conductors 65 and 69. contacts 67 of key it, conductor 17, right-hand normal contacts of key J conductors 37 and 4.8, lowermost armature and front contact of relay 33, ring contacts of plug 24.- and jack 25, ring conductor of the line B, through the operating windings of the bells at stations W and R to ground. A. two-ring signal, therefore, actuate-s the bells at both stations V7 and R. The party at W ignores the tworing si nal whereas the party at heads the signal and proceeds to answer the call.

it is to be noted from the foregoing decription that ringing current is transmitted to the station W over the ring conductor from the one-ring signaling source Z, whereas the party R is signalled ovcrthe ring conductor from the two-ring signaling source Y Had party J been the called subscriber, the operator would actuate the key 5 and in so doing put ground on the ring conductor of the cord circuit. It is to be understood that all of the keys and the apparatus depending on the actuation thereof are in normal condition. Relay 41 is then in norlnal condition and a circuit may be traced from the onering signaling source at Z over conductor 64, left-hand armature and back contact of relay 41, conductor 42 uppermost armature and back contact of relay 14, conductor 43, winding of relay 35, conductors 14 and 66, upper armature and front contact of relay 28, conductors G5 and 60, contacts 68 of key J conductor 69, lefthand normal contacts of key M righthand normal contacts of key 7 conductors 38 and 49, uppermost armature and front contact of relay 33, tip contacts of plug 24 and jack 25, tip conductor of the line B and then to ground through the operating windings of the bells at stations J and M. l he subscriber at M responds only to a tworing signal and on hearing the one-ring signal ignores it, whereas the party J recognizes the one-ring signal and proceeds to Relay 41 thereupon ener nection with the operation of key J obvious. Relay a l, as before, substitutes the two-ring signaling source at Y for the onering source at Z whereupon signaling C'rEl'- rent from the two-ring source Y is transmitted over the tip conductor of the cord circuit to actuate the bells at stations hi 2 2' J. In this case, the party 5 ignores the ring signal while the party M responds o it.

In connection with the operation of keys M 9 and J ,'it will be noted that the party M is signalled over the tip conductors from the two-ring signaling source Y, whereas the party J is signalled over the tip conductor fromthe one-ring signaling source In the foregoing description of the ri ing operation, it will be observed that relay 35 was included in each of the ringing current circuits but does not operate during the ringing period.

Having described the manner in which the four parties W, J, R and M are signalled, it will only be necessary to describe the efiect on the cord circuit apparatus when a subscriber at one of the stations responds to a s gnal as the operations in connection with the other stations are identical.

Let it be assumed that the party W responds by removing the receiver from the switchhook. In so doing. the current in the c'rcuit including relay 35 is increased to such an extent as to cause the operation of this relay. Relay 35, in operating, removes the shunt path around the winding of relay 32, whereupon relay 32 operates in series with relay 33. Relay 32, at its inner armature and front contact. connects battery directly to its winding, thereby shunting relay 33 which thereupon ieleases. Relay 33, in retracting its armatures disconnects the ringing current source from the talking conductors of the cord circuit and renders the talking conductors conductively continuous. The party at station A is now free to converse with the party V on line B.

Upon completion of the conversation, the calling subscriber restores the receiver to the switchhook at station A and thereby interrupts the circuit for supervisory relay 13 which deenergizes and releases its armature thereby causing the deenergization of relay 17. Relay 17, at its inner upper armature and back contact, establishes a circuit for supervisory lamp 55. The circuit for lam 55 is traced from grounded battery, throng 1 the filament oflamp 55. inner upper armature and back contact of relay 17 conductor 59, inner lower armature and front contact of relay 21 to ground. When the called subscriber replaces the receiver on. the switchhook, the circuit for supervisory relay 58 is tery through the filament of lamp 56. middle armature and back contact of relay '33, conductor 57, armature and back contact of relay 58, conductor to ground, through the inner lower armature and front contact of relay 21. Upon noting the lamp signals, the operator, realizing the conversation has ended, takes down the connection and re stores the apparatus to normal.

If at any time during the signaling of the called party the calling subscriber should abandon the call, relays 13 and 17 are deenergized as heretofore described and relay 17 establishes at its inner upper armature and back contact a circuit for relay 14 which may be traced from grounded battery through the winding of relay 14, conductor 54, inner upper armature and back contact of relay 17, and conductor 59, to ground, through the inner lower armature and front contact of relay 21, this relay being energized at this time owing to the insertion of plug 24 into jack 25. Relay 14 at its uppermost armature and back contact interrupts the ringing current circuit from the source at Y or Z whichever may be employed at the time. It is therefore, evident that if during th period of ringing a called subscriber, the

subscriber should abandon the call, rug current is automatically discon- 1 from the line by the operation of re- Having described. in detail the establislr nicnt of connection between the subscriber at station A and a subscriber on line B, it will now be assun'ied that this connection still. exists or in the process of completion and that a second operator at a position at which lamp 9 is located attempts to handle the call upon noting the illuminaion of lamp 9. It is to be understood that the operator at such position attempts to handle the incoming call immediately after the first operator has answered the call, otherwise the la" n 9 would have been extinguished upon 1.; insertion of plug 1.1 into jack 12.

The second operator having a cord identical with the one shown in the drawing, insorts the plug 11 into jack 50, the sleeve of jack 50 being multipled with that of ack 12 now has a busy potential thereon owing to the insertion of plug 11. of the original cord intojack 12 by the first operator. The potential on the sleeve of jack 12 has been pro rided from the battery 51 associated with the sleeve conductor Therefore, upon insertir plug 11 of the second cord into jack 50,

en gizing circuit is established for discriminating relay 16 extending from the luisy potential on the sleeve of jack 50, through elements of the second cord circuit including the sleeve contacts of plug 11, sleeve conductor armature and back contact of relay 13, winding of relay 16, conductor 53. inner lower armature and back contact of relay 17,and conductor 23 to d, through t in r l wer armature and back contact of relay 21. Relay 16, in operating, establishes an energizing circuit" for a relay 14 extending from grounded battery, through the winding of relay 14, conductor 54, and thence to ground, through the armature and front contact of relay 16. Relay 1.4, in operating, disconnects talking battery and ground from the center of repeat ing coil 15, thus preventing the operation of the supervisory relay 13 and the associated sleeve relay 17. Since relay 17 does not operate the connection of the second operators telephone set with the talking conduc of cord circuit is prevented. Relay 16, in operating, establishes energizing circuits i supervisory lamps and 5G. The circuit for lamp may be traced from grounded battery through the filai'nent of l p thence to ground over the armature and front contact of relay 16. The circuit for lamp 56 may be traced from grounded battery through the filament of lamp 56, inner lower armature and back contact of relay 33, conductor 57, armature and back contact of relay 58, conductor 59, inner upper arniatiiire and back contact of relay 17 and th ice to ground over the armature and front contacts of relay 16. It will be noted. that relay 13 is made slow tooperate in order to prevent its operation over the circuit completed therefor including the subscribers loop when plug 11 is inserted into jack 50. In order to indicate that it is slow to operate it is shown on the drawing with an arrow intercepting its armature and pointing in the direction in which it moves slowly.

It is evident from the foregoing descrip tion that a second operator cannot handle a call that is being attended to by another operator and if she should attempt to do so, she is sufficiently warned of the busy condition of the line not only by the illumination of lamps 55 and 56 but also by the absence of line noises in her head set which is sufficient to inform her that her set has not been connected to the talking conductors of the call-- ing line.

Referring now to F' 2, the method of establishing a connection between subscriber Aand subscribers on lines 13 is as follows:

Upon removing the receiver from the switchhook, the subscriber at station A effects a circuit for line relay 100 which may be traced from grounded battery through the right-hand winding clay 100, inner armature and back con of cut-off relay 101, line conductor 102, over the SlIlJSGIlbG1 S line loop, line conductor 103 outer armature and back contact of rela 101. and thence to ground through the left-nan d winding of relay 100. Line relay 100 thereupon energizes and at'its armature and front contact establishes obvious circuits for the line lamps 104 v 105 and 106. As in the preceding case, these lamps are located at different operators positions in a central office. Upon noting the illumination of the lamps any one of the operators may answer the call. assumed here that the operator before the position designated by the lamp 106 is the lirstto attempt to handle the call.

The operator inserts plug 107 into jack 108 and, in so doing, establishes an energizing circuit for slow to operate supervisory relay 109 which may be traced from grounded battery through the uppermost armature and back contact-of relay 110, lower lefthand winding of repeating coil 111, winding of relay 109, ring conductor of the cord circuit C, ring contacts of plug 107 and jack 108, over the subscribers line loop, tip contacts of jack 108 and plug 107, tip conductor of the cord circuit C, upper left-hand winding of repeating coil 111, and-thence to ground through the lowermost armature and back contact of relay 110. Relay 109, in operating, removes the discriminating test relay 112 from the sleeve of the cord and substitutes therefor the regular sleeve relay 113 which thereupon energizes over a circuit extending from grounded battery through the winding of relay 113, sleeve conductor 11%, armature and front contact of relay 109, sleeve contacts of plug 107 and jack 108, sleeve conductor 115, and thence to ground through the winding of cut-off relay 101. Relays 101 and 113 energize in the circuit just traced. Relay 101, in operatin disconnects the line relay 100 from the su scribers line conductors which relay thereupon releases and opens the circuit for lamps 104, 105 and 106 which are thereby extinguished. Relay 113,,in operating, connects at its inner upper and innermost upper armatures and front contacts, the operators telephone set (not shown but designated by OT) with the talking conductors of the cord circuit by way of the normal contacts of relay 20. At its lowermost armature and front contact, relay 113 establishes an energizing circuit for the position register 116 which may be traced from grounded battery through the operating windings of register 116, conductor 117, lowest armature and front contact of relay 113, conductor 118, andv thence to ground, through the armature and back contact of relay 119. The functions of the position register as stated hereinbefore are well known in the art and need not be explained here. Relay 113 at its inner lower armature opens the circuit for supervisory lamp 123 to prevent its illu1ninatioii at this time and also at its uppermost armature and front contact connects the busy test lead tothe tip conductor of the calling end of the cord circuit. I

The operator now converses with the calling subscriber and ascertains the nature of the call. Upon learning that a subscriber on line B is desired, the operator inserts It will be the calling plug 121 of cord G into jack 122 associated with the called subscribers line.

Upon insertion of plug 121 into jack 122, a circuit is established extending from grounded battery through the middle armature and back contact of relay 110, conductor 195, winding of relay 120, conductor 121, right-hand windingof relay 119, conductor 125, and sleeve contacts of plug 121 and jack 122 to ground through the winding of the cut-off relay associated with jack 122. An energizing circuit is also established for relay 119 extending from grounded battery through the left-hand winding or relay 119, conductor 125, sleeve contacts of plug 121 and jack 122, and thence to ground through the winding of the cut-off relay associated with ack 122. Relays 120 and 119 energize in the circuits just traced. Relay 120 in operating disconnects at its lowest and up per-most armatures and back contacts the operators telephone set from the talking strands of the cord circuit and carries the talking strands to the contacts of relay 128. Belay 119 interrupts the energizing circuit for position register 116 and at the same time establishes a circuit for relay 126 which may be traced from grounded battery through the winding of relay 126, conductor 12'? and thence to ground over the armature and front contact or relay 119. Relay 126 thereupon energizes and at its upper armature and front contact makes the tip conductor of the cord circuit continuous and disconnects the busy test lead 180 from the tip conductor of the cord. Relay 126 also establishes an energizing circuit for relay 128 which may be traced from grounded battery through the winding of relay 128, left-hand armature and back contact of relay 14:2, conductor 141-3, armature and back contact of relay 134,, conductor 14:4, and thence to ground, through the make contacts and lower armature of relay 126. Relay 128 in operating connects conductors 140 and 1 11 associated with the four-party ringing keys to the ring and tip conductors of the cord circuit. Relay 142 does not energize at this time owing to the shunt about its winding which includes conductor 144, the armature of relay 13 1 and conductor 143. The connection is now fully established and the operator proceeds to ring the calledfor subscriber in the following manner.

As in the preceding case, Fig. 2 discloses a four-party semi-selective ringing system and the manner in which the signaling apparatus at the different stations is operated is as follows:

It is to be understood that two parties are signaled on the ring conductor and two on the tip conductor, one of the parties on the ring conductor answering a two-ring signal and the other party answering a single ring signal while one party on the tip conductor responds to a two-ring signal while the other replies to a single ring signal.

Relay 126 in operating, as heretofore described, establishes a circuit for relay 150 which is traced from grounded battery through the live segment and brush of pickup interrupter X, when such interrupter is in its pick-up position, conductor 151, the break contacts of relay 150, conductor 152, right-hand armature and back contact of relay 142, conductor 153, winding of relay 150, conductor 154, and thence to ground through the lower armature and front contact of relay 126. Relay 150, in operating, bridges the conductors and 164 for a purpose hereinafter to be described and also establishes a locking circuit for itself which may be traced from grounded battery through its right-hand armature and front contact. conductor 152, right-hand armature and back contact of relay 142, conductor 153, winding of relay 150, conductor 154, and thence to ground through the front contact and lower armature of relay 126.

Assuming that the party 1V is the desired subscriber, the operator actuates ringing key W which places ground on the tip conductor of the line and also establishes a circuit extending from the grounded one-ring signaling current source at Z, over the live segment and brush of the interrupter at Z, conductor 161, left-hand armature and back contact of relay 133, winding of relay 134, conductor 135, contacts 136 of key W conductor 127 right-hand normally closed contacts of key R conductor 138, right-hand normally closed contacts of key J conductors 139 and 140, lowermost armature and front contactof relay 128, ring contacts of plug 121 and jack 122, the ring conductor of the line B, and thence to ground through the operating windings of the bells at stations W and R. The bells are actuated from a one-ring signaling source and since the party at W only replies to a one-ring signal, the receiver thereat is removed. The party at R, replying only to a two-ring signal, does not heed the one-ring signal.

It will be assumed now that the party R is desired and the operator actuates the key R In so doing an energizing circuit for relay 133 is established, which may be traced from grounded battery through the right-- hand armature and front contactof relay 150, conductor 152, right-hand armature and back contat of relay 142,'conductor 153, winding of relay 133, conductors 162 and 160, and thence to ground through the lefthand contact of key R Relay 133, in operating, disconnects the one-ring signal source fromconductor 135 and substitutes therefor the two ring signal source from interrupter Y. Ringing current is then transmitted from the one-ring source at Y over the ringing current is transmitted from the two-ring signaling source at Y, the subscriber at ll only, responds to the signal.

If the party at J is the required subscriber, the operator actuates key J all other keys being released and relay 133 being deenergized. Ground is ,thereby connected to the ring conductor of the cord circuit. Oneaing signaling current is then transmitted from the source at Z over a circuit traced from this source and including conductor 161, left-hand armature and back contact of relay 133, winding of relay 134, conductors 135 and 163, lefthand armature and front contact of relay 150, conductor 164, left-hand contacts of key J right hand normally closed contacts of key M conductor 166, left-hand normally closed contacts of key 1' conductors 142 and 141, middle armature and frontcontact of relay 128, upper armature and front con tactof relay 126, tip contacts of plug 121 and jack 122, over the tip conductor of the line B and thence to ground, through the operating windings of the bells of stations J and M. The subscriber at J hearing the one-ring signal answers the call whereas the1 subscriber at M does not heed the signa If the subscriber at M is desired the operator actuates key 1 199 and establishes a circuit for relay 133, as described in connection with the actuation of key R This relay substitutes the two-ring signaling source at Y for the one-ring signaling source normally associated with the conductor 135. One-ring signaling current thereupon transmitted over the tip conductor of the line to actuate the bells at stations M and J The subscriber at J does not reply to the two-ring signal, whereas the party at M does The desired party, upon hearing the signal, removes the receiver from the switchhook and in so doing increases the current in the circuit including relay 134 to such an extent that this relay operates and at its armature and back contact removes the shunt around the winding of relay 142. Re lay 142 thereupon operates and connects battery directly with the winding of relay 128 thereby neutralizing the effect of the battery normally associated with this Wind- 7 lower inner armature and back contact of,

Relay 128 deenergizes thereby renderthe talking conductors of the cord cirnit continuous.

In removing the receiver from the switchhook, a circuit is established for supervisory relay 127 which may be traced trom grounded battery through the lower righthand winding of repeating coil 111, winding of relay 127, lowermost armature and front contact or" relay 120, conductor 130, lowermost armature and back contact of relay 128, ring contacts of plug 121 and jack 122 over the subscribers line loop, the tip contacts of jack 122 and plug 121, upper armature and front contact of relay 126,

middle armature and back contact of relay 128, conductor 129, uppermost armature and front contact of relay 120, and the upper right-hand winding of repeating coil 111 to ground. Relay 127, in operating, opens the circuit for supervisory lamp 131 which otherwise would have been illuminated from the source associated with the upper armatures of relay 110 upon the release of re lay 12s.

It is to be noted that no signal is given the operator to inform her when the called subscriber has responded.

lVhen the conversation has ended, the calling subscriber replaces the receiver on the switchhook thereby releasing supervisory relay 109. Relay 109 in deenergizing interrupts the circuit for relay 113 which, in releasing, closes a. circuit from grounded battery, through the filament of lamp 123,

relay 113 to ground, through the armature and front contact oi relay 119. Lamp 123 is illuminated in this circuit and informs the operator that the calling subscriber has terminated the conversation and has replaced the receiver on the switchhook.

lVhen the called subscriber replaces the receiver on the switchhook, supervisory relay 12. is deenergized whereu 3011 a circuit is established from grounc ed battery through the middle armature and back contact of relay 110, conductor 195, middle armature and trout contact of relay 120, armature and back contact of relay 127, conductor 190, uppermost armature and back contact of relay 12S, and thence to ground through the filament of supervisory lamp 131. Lamp 131 is illuminated in this circuit and notifies the operator that the called subscriber has replaced the receiver on the hook and the operator thereupon proceeds to take down the connection.

As in the description of the system shown in Fig. 1, should an operator attempt to plug into a busy line, the discriminating test relay 112 would operate from the busy potential on the sleeve of the jack through the sleeve of the plug to ground at the armature and normal contactof relay 119. Re-

lay 112, in operating, establishes an obvious circuit for relay 110 which disconnects ground and battery from the tip and ring conductors respectively 01 the answering end of the cord circuit. The regular sleeve rela Y 113 is prevented from operating, since slow to operate supervisory relay 109 does not operate, thereby preventing the operators telephone set from being automatically connected to the talking conductors of the cord circuit. Supervisory lamps 131. and 123 at the calling and answering ends 01 the cord circuit are illuminated, lamp 131 over a circuit traced from grounded battery through the middle armature and front contact of relay 110, conductor 191, middle armature and back contact of relay 120, armature and contact of relay 127, conductor 190, uppermost armature and back contact of relay 128 and to ground through the filament of lamp 131. Lamp 123 is illuminated over a circuit extending from grounded battery through the filamentof lamp 123, thence to ground over .the armature and front contact of relay 112.

It is evident from the foregoing description that the second operator is sufficiently warned when she attempts to plug into a busy line as well as is actually prevented from interfering with the establishment oi" the connection by the first operator.

What is claimed is:

1. In a telephone system, a calling line, operators link circuits comprising a pair of talking conductors and a third conductor, a source of current for said link circuits, and means controlled over said third conductor for disconnecting said source of current from one of said link circuits when more than one of said link circuits are conneeted to said calling line.

2. In a telephone system, a calling line, a link circuit comprising a pair of talking conductors and a third conductor, a source of current for said link circuit, a slow operating relay included in one of said talking conductors and means normally associated with the third conductor of said linl; circuit for disconnecting said source or current from said link circuit, said means being under the control of said slow operating relay.

3. In a telephone system, a calling line, link circuits comprising a pair of talking conductors and a third conductor, a current source in each of said link circuits, an operators telephone for said link circuits, a plurality of signals for each of said link circuits and means included in said third conductor responsive to the association of more than one of said link circuits with said calling line, whereby said current source is disconnected from its associated link circuit, said operators telephone is prevented from association with its respective rink ciation o'l more than one of said link circuits with one of and lines.

In a telephone system, a telephone line, terminating at a plurality of positions at a switchboard, a plurality of link circuits ateach of said positions for answering calls for said lines, each of said link circuits c I ing a pair of talking conductors and a third conductor, a slow operating relay included in one of the talking conductors in each 01" said link circuits and means included in the third conductor of each of said link circuits and controlled by said slow operatg relay, for preventing the operative assoc ation oil? more than one of said link circuits with said telephone line.

6. In a telephone system, a lousy telephone line, a link circuit having a calling and an answering plug, a calling supervisory sig nal associated with said calling plug, an answering supervisory signal associated with said answering plug, and means responsive to the connection of said answering plug of said link circuit to said busy. telephone line for operating both said sig nals.

7. In a telephone system, acalling line, operators link circuits comprising a pair of talking conductors and a third conductor, a. source of current normally associated with each or said link circuits, and means ccn trolled over said third conductor for disconnecting said source of current from one of said link circuits when more than one of said link circuits are connected to said calling line.

8. In a telephone system, a calling line, a source of current, operatcrs link circuits each having an answering and a calling end, each oi said link circuits comprising a pair of tal ring conductors and a third conductor and having the talking conductors of the answering end normally connected to said source or' current, and each said link circuit having a relay normally associated with said third conductor effective upon its operation to open said normal connection between said talking conductors and said source of current, each of said relays being responsive to the connection of the answersource of current 'from one of said link c1r- (nits when more than one (it said link circuits are connected with said calling line.

10. In a telephone system, a calling line, operators link circuits comprising two inductircly coupled sections, each section having a pair of talking conductors and a third conductor, a source of current normally as sociated with one of said sections, and n'icans associated with said third conductor and operating only upon association of more than one of said link circuits with said calling line for disconnecting said source of current from said section.

11. In a telephone system, a calling line, operators link circuits having answering and calling slugs and comprising a pair of talking conductors and a third conductor, an operators telephone set for association with said link circuits, means including a slow-operating, relay connected to the talking conductor of theanswering plug 01? each of said link circuits, for connecting the op erators telephone set to a corresponding link circuit, and means including a second relay normally connected to said third conductor for controlling said slow-operating relay for preventing the association of said telephone set with other link circuits when more than one of said link circuits are con; nectedto said calling line.

12; In a telephone system, a calling line, link circuits having answering and calling plugs and each comprising a pair or talking conductors and a third conductor, a si naling device for each of said plugs, a slow acting relay in the circuit o'l one of said talking conductors, andmeans normally associated with the third conductor ot said link circuits and controlled: by said slowoperating relay for causing the signaling devices of one of said link circuits to be operated when more; than one of said link circuits are connected with said calling line.

In testimony whereof, I have signed my name to this specification this 9th day of October, 1922.

RAND S. BAILEY. 

